The W.M. Keck Center for Cellular Imaging (KCCI), an internationally recognized center for advanced light microscopy imaging that is particularly known for protein-protein interaction imaging, is requesting a "Frequency-domain Fluorescence Lifetime Imaging Microscopy (FD-FLIM)" system. KCCI is a University wide imaging facility and the requested instrument will benefit the basic and clinical science investigators of this university, and particularly the 7 participating federally funded investigators. The instrument will be housed in the KCCI, located within walking distance of all the participating investigators. The central theme of the research to be performed on the requested FD-FLIM is the study of protein-protein interactions in live cells and other cellular imaging including IQGAPs and the Cell Biology of Alzheimer's Disease, characterization of new FRET reference standards, glutamine FRET sensors, RNA-protein interactions, and monitoring oxygen, pH sensors in polymers. The requested instrument, confocal FD-FLIM system is unique and, providing users the ability to tune the excitation wavelengths (through software) to match exactly the fluorophores in their experimental samples. The user no longer needs to adapt the experiment to the laser lines available on the FD-FLIM system;the computerized monochromator tunable supercontimuum laser system adapts to the particular experiment. There is currently no system available at the University of Virginia that has a tunable (400-2500 nm) laser FD-FLIM imaging capability and collects FLIM images in few seconds. This is essential for our core investigator group, and will also be critical for training other investigators interested in the study of protein associations in living cells and tissues. The KCCI is recognized for its annual hands-on-training FRET course, held for the past eight years at the University of Virginia. To date, 224 scientists (336 registered), from the United States as well as scientists from 25 countries have participated in the FRET workshop. In summary, the requested instrument will provide the research community at the University of Virginia with a level of imaging capability that is not currently available, and this will enhance significantly ongoing and future research.